1. Field of the Invention
The present invention relates to a polyether polyurethane. More particularly, the present invention is concerned with a polyether polyurethane comprising (A) at least one polyisocyanate having two or more isocyanate groups, which is selected from the group consisting of an aromatic polyisocyanate and an aliphatic polyisocyanate; (B) a specific polyoxytetramethylene glycol (PTMG); and (C) at least one chain extender selected from the group consisting of a C2-C10 polyol having two or more hydroxyl groups and a C2-C10 polyamine having two or more amino groups. The polyether polyurethane of the present invention exhibits excellent properties including high elastic modulus, excellent elastic properties at low temperatures and high flexibility, as compared to the conventional polyether polyurethanes. By virtue of these excellent properties, the polyether polyurethane of the present invention can be advantageously used in various application fields where conventional polyether polyurethanes are used. Further, the present invention is also concerned with a urethane prepolymer comprising (A) at least one polyisocyanate having two or more isocyanate groups, which is selected from the group consisting of an aromatic polyisocyanate and an aliphatic polyisocyanate; and (B) a specific polyoxytetramethylene glycol (PTMG), wherein the urethane prepolymer has terminal isocyanate groups.
2. Prior Art
In the production of polyether polyurethanes, various types of diols are used to control the properties thereof. For example, a low molecular weight diol is used in combination with a high molecular weight diol, such as a polyether diol, a polyester diol or a polycarbonate diol. Specific examples of polyether diols include polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene glycol and modified high molecular weight diols obtained therefrom. Of the above-exemplified polyether diols, polyoxytetramethylene glycol has been used as a component constituting a soft segment of a shaped polyether polyurethane article or a polyether polyurethane elastic fiber since a long time ago.
A polyether polyurethane is produced from a polyisocyanate, a high molecular weight diol and a low molecular weight diol as main raw materials, and is a block copolymer having a soft segment composed mainly of the high molecular weight diol and a hard segment composed mainly of the polyisocyanate and the low molecular weight diol. By virtue of such structure, the polyether polyurethane exhibits rubber elasticity. The chemical composition, length of the polymer blocks, and secondary and tertiary structures of the polyether polyurethane depend mainly on the types of the polyisocyanate and the high molecular weight diol used, and have a large influence on the physical properties of an ultimate polyether polyurethane product. Especially, the choice of the soft segment is a very important factor in fields where a product obtained from a polyether polyurethane, such as an elastic fiber or a polyurethane elastomer, is required to have excellent and precisely controlled mechanical properties and visco-elastic properties.
As a conventional technique for obtaining a polyoxytetramethylene glycol (PTMG) which has been used as a high molecular weight diol, a method disclosed in Unexamined Japanese Patent Application Laid-Open Specification No. 59-215320 (corresponding to U.S. Pat. No. 4,568,775 and EP 126471) is known. Further, Unexamined Japanese Patent Application Laid-Open Specification No. 61-123626 (corresponding to U.S. Pat. No. 4,658,065 and EP 158229) and Unexamined Japanese Patent Application Laid-Open Specification No. 59-221326 (corresponding to U.S. Pat. No. 4,568,775 and EP 126471) have a description concerning the molecular weight distributions of the produced PTMG""s. With respect to the techniques for removing the oligomers contained in a PTMG, Unexamined Japanese Patent Application Laid-Open Specification No. 61-123629 (corresponding to U.S. Pat. No. 4,677,231 and EP 181621) discloses a method in which a thin film evaporator is used, and Unexamined Japanese Patent Application Laid-Open Specification No. 60-108424 discloses a method in which oligomers are separated from the PTMG by using water and an alcoholic solvent. In addition, with respect to the techniques for adjusting the content of a polymerization catalyst remaining in a PTMG, Unexamined Japanese Patent Application Laid-Open Specification No. 61-118420 (corresponding to U.S. Pat. No. 4,677,231 and EP 181621) and Unexamined Japanese Patent Application Laid-Open Specification No. 61-115934 (corresponding to U.S. Pat. No. 4,677,231 and EP 181621) disclose a method in which a hydrocarbon or a halogenated hydrocarbon as an organic solvent is added to a PTMG to thereby separate the residual catalyst therefrom; and Unexamined Japanese Patent Application Laid-Open Specification No. 61-123629 (corresponding to U.S. Pat. No. 4,677,231 and EP 181621) discloses a method in which an adsorbent is used to remove the catalyst.
The characteristics (such as molecular weight, molecular weight distribution, oligomer content and residual catalyst content) of the PTMG used as a raw material for a polyether polyurethane are considered as important factors which affect the quality of the final polyether polyurethane. However, heretofore, no details are known in the art about how the characteristics of the PTMG influence the physical properties of the final polyether polyurethane. In addition, no polyether polyurethanes are known, which have been adjusted, by strictly controlling the characteristics of the raw material PTMG, so as to have a good balance of various excellent properties.
Nowadays, polyether polyurethane is an important material which is used in a wide variety of fields, and the application field thereof is expected to become more extensive. Accordingly, there has always been a demand for improvement in the quality of the polyether polyurethane. Further, improvements in different properties of the polyether polyurethane are, respectively, desired in different application fields. For example, a polyether polyurethane used as a thermoplastic elastomer is required to exhibit high elastic modulus, excellent characteristics at low temperatures, small compression set, excellent surface touch with respect to an ultimate shaped product produced therefrom, and convenience in practical use of a coating composition containing the polyether polyurethane. Similarly, in the industrial fields related to a flexible foam and a rigid foam, an RIM (Reaction Injection Molding) product, an R-RIM (Reinforced Reaction Injection Molding) product, a coating composition, an adhesive, a binder, a sealant, a fiber stock, an artificial leather and a wide variety of other polyurethane products, and in various other industrial fields related to polyurethane urea products, there has been a demand for the improvements in the properties of a polyether polyurethane.
In this situation, the present inventors have made extensive and intensive studies with a view toward solving the above-mentioned problems. As a result, it has unexpectedly been found that a polyether polyurethane, which comprises (A) at least one polyisocyanate having two or more isocyanate groups, which is selected from the group consisting of an aromatic polyisocyanate and an aliphatic polyisocyanate, (B) a polyoxytetramethylene glycol (PTMG) having a specific molecular weight, a specific molecular weight distribution and a specific content of high molecular weight molecules, which PTMG, notwithstanding low viscosity thereof, exhibits high heat resistance, and (C) at least one chain extender selected from the group consisting of a C2-C10 polyol having two or more hydroxyl groups and a C2-C10 polyamine having two or more amino groups, exhibits high elastic modulus, excellent elastic properties at low temperatures and high flexibility, as compared to the conventional polyether polyurethanes.
The present invention has been completed, based on this novel finding.
Accordingly, it is an object of the present invention to provide a polyether polyurethane having high elastic modulus, excellent elastic properties at low temperatures and high flexibility.
It is another object of the present invention to provide a urethane prepolymer which can be used as a raw material for obtaining a polyether polyurethane having high elastic modulus, excellent elastic properties at low temperatures and high flexibility.
The foregoing and other objects, features and advantages of the present invention will be apparent to those skilled in the art from the following detailed description and appended claims taken in connection with the accompanying drawings.